The present invention relates to a crane control with active heave compensation for a crane arranged on a floating body, which includes a hoisting gear for lifting a load hanging on a rope.
Such crane controls are required to compensate the undesired influences of the sea waves on the movement of the load, which otherwise impair the safety and accuracy of the hoisting operation, in a crane mounted on a floating body, such as a ship, a semi-submersible platform or a bark.
For the installation of offshore wind parks and underwater extraction plants, an increasing demand of floating cranes exists, so that crane controls with heave compensation have a particular importance. Such crane control should provide for a safe, exact and efficient operation of the crane also under poor weather conditions with great heave, in order to minimize the weather-related downtimes. In addition, the safety of both operating personnel and equipment should be ensured.
If a crane is mounted on a floating body, a movement of the floating body due to heave leads to a movement of the load suspension point of the load hanging on the crane. On the one hand, this leads to a corresponding movement of the load, which impedes the exact positioning of the load and endangers the assembly personnel. For instance, if a rotor should be mounted on an offshore wind turbine, an extremely accurate positioning of the rotor blades on the hub is required, where the same must be screwed by the mechanics. Here, every uncontrolled movement of the rotor blade due to heave can have devastating consequences. In addition, the movement of the load suspension point can lead to critical force peaks in the rope and in the crane, which must be considered in particular in the case of deep-sea hoisting operations.
In cranes in accordance with the prior art it has already been attempted to at least partly compensate the movement of the load during sea movements. On the one hand, passive systems are known, in which the heave movement should be compensated passively by the construction of crane and hoisting gear. There are also known active controls, in which the movement of the load suspension point generated by the heave movement should be compensated by active countersteering. However, none of the known systems has led to a really satisfactory solution.